The need to prevent a vehicle from moving during loading and unloading operations has been addressed by a variety of different techniques. The most basic is the wheel chock, a wedge placed in front of the wheels of the truck. While simple, they are often misplaced, dislodged or slip. Given those known deficiencies a class of mechanical restraints evolved which were either mounted on the dock face or on the approach and moved to engage the truck by interaction with the ICC bar, mounted on the rear of the vehicle. The majority of mechanical vehicle restraints currently in use contact the ICC bar of the transport vehicle to prevent it from moving away from the loading dock by providing a mechanical member resisting vehicle movement away from the dock. While this method is suitable for the majority of trailers, there are several configurations which cannot be secured by the traditional vehicle restraint. These include missing, bent or extremely low ICC bars, and hydraulic tail gates or other special equipment attached to the rear of the vehicle.
Given this problem of missing or irregular ICC bars, renewed interest has taken place in the industry to restrain by chocking the wheels, albeit by mechanical means. Examples of devices which do not rely on the presence of an ICC bar are typified by U.S. Pat. Nos. 4,969,792 and 5,249,905. In these devices the apparatus is buried in a pit in the driveway which causes a wheel chock to be raised from a stored position and drawn rearward to contact the front of a wheel. While providing an effective mechanism to prevent the vehicle from moving away from the dock, these devices have several limitations. First, because it is buried in the driveway, the unit is expensive to install and requires a drain to prevent it from filling with water. Because it chocks only one wheel of the trailer, it may result in lateral loads on the front "landing gear" and may not be effective in preventing "landing gear" collapse. Also, with the great variety of axle placement on trailers, it will be unable to operate if a wheel is positioned over the stored location of the chock. Finally, because it is buried in a pit in the driveway, it may be difficult to service or repair, and cannot be readily moved to a new location. Another automatic chocking device built by Rite-Hite Corporation is mounted on the driveway, but it forms an obstacle which the truck must drive over, and which thus impedes snow removal. In addition, it also would be unable to operate if a wheel is positioned over the stored location of the chock.